1. Field of the Invention
The present invention relates to a heat exchanger made of aluminum alloy used as a heater core which is incorporated into an air conditioning apparatus for a car to heat the air that is used to condition the air in the interior of the car.
The present application is based on Japanese Patent Application No. Hei. 11-116800, which is incorporated herein by reference.
2. Description of the Related Art
Conventionally, it has been widely known that a tank, a heat transmission tube and a fin which are used to form a heater core are respectively made of plate members which are formed of aluminum alloy. Also, of the above three component members, in the tank, there is employed a structure in which the tank is composed of a combination of a seat plate and a tank main body respectively produced by enforcing plastic working such as press working on their respective mother or blank plate members made of aluminum alloy; that is, conventionally, this tank structure is also widely known, as disclosed in, for example, Japanese Patent Publication Nos. Hei. 7-280488, Hei. 7-305990, Hei. 8-327279, and Japanese Utility Model publication Sho. No. 62-70283.
Of the aluminum-alloy heat exchangers respectively disclosed in the above-cited publications, the aluminum-alloy heat exchangers especially disclosed in Japanese Patent Publication No. Hei. 8-327279 and Japanese Utility Model Publication No. Sho. 62-70283 respectively employ the following structure. In the outer peripheral edges of the tank main body and seat plate, there are formed hanging walls or vertical walls so as to extend over the whole periphery of the present outer peripheral edges, and the thus formed tank main body and seat plate are combined together in a wafer cake. In the case of such structure, however, when the plate members made of aluminum alloy, that is, the mother or raw members are deformed plastically to thereby form the above-mentioned tank main body and seat plate, there is required a relatively large force. This increases the size of the facilities that are used to execute press working, which in turn increases the cost of the facilities and thus makes it difficult to reduce the cost of the aluminum-alloy heat exchanger. Also, in order to be able to change heat exchange performance, when trying to obtain aluminum-alloy heat exchangers having different width dimensions, it is necessary to change a press mold itself to an entirely different one, which leads to an increase in the cost of the product. In the case of production of a large kinds of aluminum-alloy heat exchangers, the cost of the products becomes especially high.
On the other hand, in the aluminum-alloy heat exchangers respectively disclosed in Japanese Patent Publication Nos. Hei. 7-280488 and Hei. 7-305990 of Heisei, a tank main body and a seat plate respectively formed in a gutter shape are combined together to form a tubular-shaped member, and two openings formed at the two ends of the tubular-shaped member are closed by end plates which are produced separately from the tank main body and seat plate. In the case of this structure, there is necessary a small force when the plate members made of aluminum alloy used as the blank members are deformed plastically to thereby form the above-mentioned tank main body and seat plate. Thanks to this, when the plastic deformation is executed by press working, it is possible to use the facilities that are small in capacity and size and it is also possible to work the plate members consecutively by press working, which can reduce the cost of the facilities and thus can reduce the cost of the aluminum-alloy heat exchangers. Further, since the lengths of the tank main body and seat plate can be adjusted easily, even when producing aluminum-alloy heat exchangers different in the width dimension thereof, the press mold as it is can be used. That is, even in the case of production of a large kinds of aluminum-alloy heat exchangers, an increase in the cost of the products can be controlled down to a low level.
However, in the above-mentioned conventional aluminum-alloy heat exchangers respectively disclosed in Japanese Patent Publication Nos. Hei. 7-280488 and Hei. 7-305990 of Heisei, no account is taken of the followings: that is, how to enhance the efficiency of the assembling or combining operation and how to secure sufficient corrosion resistance. Specifically, referring to the enhancement in the efficiency of the assembling operation, in the conventional aluminum-alloy heat exchangers respectively disclosed in the above-mentioned publications, no restrictions are placed on the assembling direction of the end plates with respect to the tank main body and seat plate. Therefore, the end plates can be assembled to the tank main body and seat plate in any direction.
On the other hand, generally, an aluminum-alloy heat exchanger is structured by connecting together the respective component members thereof by brazing. Here, brazing material used for the brazing connection is previously applied (clad) on the surfaces of the respective component members. That is, each of the component members is made of a clad member which is composed of core material consisting of aluminum alloy having a high melting point and brazing material consisting of aluminum alloy having a low melting point cladded on the surface of the core material. And, in a state where the respective component members are assembled together, they are heated in a heating furnace up to a temperature slightly higher than the melting point of the brazing material to thereby melt the brazing material, so that the mutually adjoining component members can be connected together by brazing.
Because the brazing material contains a large quantity of Si, it is not sufficiently resistant against corrosion and, especially when the brazing material touches corrosive fluid, so called pitting is easy to occur in which the corrosion of the brazing material will progress locally in the thickness direction thereof. In case where the aluminum-alloy heat exchanger is used as a heater core, the coolant of an engine flows in the interior portion of the tank; and, since the coolant contains iron ions and copper ions, the coolant act as the corrosive fluid with respect to the aluminum alloy. For this reason, it is necessary to avoid positioning the surface of the end plate with the brazing material cladded thereon on the inner surface side of the tank. However, in the case of the aluminum-alloy heat exchangers respectively disclosed in the above-cited publications, since the end plate can be assembled in any direction, unless special account is taken of the assembling direction of the end plate in the assembling operation, there is a possibility that the end plate can be positioned on the inner surface side of the tank. Therefore, when trying to secure sufficient durability in the aluminum-alloy heat exchanger, the operation to assemble together the respective component members provides a poor efficiency, which increases the cost of the aluminum-alloy heat exchanger.